Occipital intermittent rhythmic delta activity only following eye closure in atypical CNS Salmonellosis

Occipital intermittent rhythmic delta activity (OIRDA) in pediatric focal epilepsies: A case series

In this case series, we have identified an atypical pattern of OIRDA (Occipital intermittent rhythmic delta activity) on the electroencephalograms (EEGs) of three pediatric patients with self-limited focal epilepsies, including Childhood Epilepsy with Centrotemporal Spikes (CECTS), and Panayiotopoulos syndrome (PS). Previously, OIRDA was described as a symmetric sinusoidal occipital-maximal activity, often associated with childhood idiopathic generalized epilepsies, although it was also reported among other physiologic or pathological entities including focal epilepsy. We have observed in our case series that OIRDA, without prominent field effect, is lateralized or maximal on the hemispheric side ipsilateral to the more defining epileptiform discharges in these focal epilepsies. They also exhibit a notched morphology due to the intermixed sharp wave activities, although the sharp waves are not occurring repetitively. This report provides additional evidence that OIRDA can be associated with a spectrum of idiopathic focal epilepsies and may suggest a cortical origin of OIRDA in these patients as opposed to a hypothesized subcortical generator in patients with primary generalized absence epilepsy, even though further investigation is warranted for either hypothesis.

Clinical associations of occipital intermittent rhythmic delta activity

Association of occipital intermittent rhythmic delta activity with absence seizures has been well documented in the published literature. Two recent studies have also described an association with focal seizures. After obtaining approval from our Institutional Review Board, all electroencephalograms with occipital intermittent rhythmic delta activity at our institution between July 1, 2006 and December 31, 2009 were identified. Charts of these patients were reviewed to collect clinical data. A matched comparison group was assembled. Thirty-one of the patients who met criteria had evaluable clinical data. Fifteen had generalized seizures (9 absence; 2 tonic-clonic; 3 absence and tonic-clonic; 1 absence, tonic-clonic, myoclonic, and atonic). Eleven had focal seizures. One had both generalized tonic-clonic and focal seizures. Events in 1 were nonepileptic in nature. Documentation was inadequate for seizure classification in 3. There was a statistically significant difference between the study and comparison groups for absence seizures, but not for focal seizures.

Intermittent rhythmic delta activity patterns

Intermittent rhythmic delta activity is a typical EEG pattern that was originally described by W.A. Cobb in 1945 (J Neurol Neurosurg Psychiatr 1945;8:65-78). It may be classified into three distinct forms according to the main cortical region involved on the EEG: frontal (FIRDA), temporal (TIRDA), and occipital (OIRDA) intermittent delta activity. This article is a review of the main aspects of these patterns, with a special focus on EEG features and problems that may be encountered during interpretation of these patterns. In contrast to FIRDA and OIRDA, TIRDA is highly indicative of ipsilateral pathology. OIRDA and TIRDA are highly correlated with epilepsy, whereas FIRDA is a rather nonspecific EEG pattern.

Clinical Correlates of Occipital Intermittent Rhythmic Delta Activity (OIRDA) in Children

PURPOSE

The clinical significance of occipital intermittent rhythmic delta activity (OIRDA) on the electroencephalogram has not been fully established. Recent studies suggest that this pattern occurs almost exclusively in children and is probably of epileptic origin in most cases. We sought to characterize the electrographic features and clinical correlates of occipital intermittent rhythmic delta activity.

METHODS

A review of 697 consecutive pediatric electroencephalograms detected occipital intermittent rhythmic delta activity in 24 studies. Mean patient age was 7.96 years.

RESULTS

Recent convulsions and absence seizures constituted the main indications for the study. Concomitant, independent epileptiform activity was noted in half of the cases. This activity was focal in all but one case. Conversely, in most cases of absence seizures, epileptiform activity intermixed with occipital intermittent rhythmic delta activity. Furthermore, the frequency of the occipital rhythmic discharges in studies of children with absences was generally faster (3-4 Hz) than in localization-related epilepsy (2-3 Hz). Most patients were awake when occipital intermittent rhythmic delta activity occurred. Chronic encephalopathy was seen in one child only. Analysis of neuroimaging studies in eight cases revealed no structural pathology associated with occipital intermittent rhythmic delta activity.

CONCLUSIONS

Occipital intermittent rhythmic delta activity is probably an epileptiform pattern, although it is noted occasionally in encephalopathic children. Its electrographic characteristics appear to differ between localization-related epilepsy and primary generalized epilepsy, particularly absence seizures.